1. Operating System

1. Operating System - Overview

Definition: An operating system is a program that acts as an interface between the user and the computer hardware and controls the execution of all kinds of programs.

Memory Management: Memory management refers to the management of Primary Memory or Main Memory. It keeps track of primary memory, i.e., what part of it is in use by whom, what parts are not in use. It allocates and de-allocates the memory when a process requests it to do so.

Processor Management: Processor Management keeps track of the processor and the status of a process. The program responsible for this task is known as a traffic controller. It is responsible for allocating and de-allocating the processor (CPU) to a process.

Device Management: An Operating System manages device communication via their respective drivers. Device Management keeps track of all devices. The program responsible for this task is known as the I/O Controller. It decides which process gets the device when and for how much time. It allocates and de-allocates the device in the most efficient way.

File Management: A file system is normally organized into directories for easy navigation and usage. These directories may contain files and other directions. File Management keeps track of information, location, uses, status, etc. The collective facilities are often known as a file system.

Security: By means of passwords and similar other techniques, it prevents unauthorized access to programs and data.

Error Detecting Aids: Production of dumps, traces, error messages, and other debugging and error detecting aids.

Job Accounting: Keeping track of time and resources used by various jobs and users.

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7.Operating System - Memory Management

Process Address Space: The process address space is the set of logical addresses that a process references in its code. Static vs Dynamic Loading: The choice between Static or Dynamic Loading is to be made at the time of the computer program being developed. If you have to load your program statically, then at the time of compilation, the complete programs will be compiled and linked without leaving any external program or module dependency. If you are writing a dynamically loaded program, then your compiler will compile the program and for all the modules which you want to include dynamically, only references will be provided and the rest of the work will be done at the time of execution. At the time of loading, with static loading, the absolute program (and data) is loaded into memory in order for execution to start. If you are using dynamic loading, dynamic routines of the library are stored on a disk in re-locatable form and are loaded into memory only when they a...

8. Operating System - Virtual Memory and Input/Output

Definition: A computer can address more memory than the amount physically installed on the system. This extra memory is actually called virtual memory and it is a section of a hard disk that's set up to emulate the computer's RAM. The main visible advantage of this scheme is that programs can be larger than physical memory. Virtual memory serves two purposes. First, it allows us to extend the use of physical memory by using disk. Second, it allows us to have memory protection, because each virtual address is translated to a physical address. Demand Paging: A demand paging system is quite similar to a paging system with swapping where processes reside in secondary memory and pages are loaded only on demand, not in advance. Page Replacement Algorithm: Page replacement algorithms are the techniques using which an Operating System decides which memory pages to swap out, write to disk when a page of memory needs to be allocated Reference String: The string of memory references i...

9. Operating System - Extra

Interrupt: In system programming, an interrupt is a signal to the processor emitted by hardware or software indicating an event that needs immediate attention. Trap: In computing and operating systems, a trap, also known as an exception or a fault, is typically a type of synchronous interrupt caused by an exceptional condition (e.g., breakpoint, division by zero, invalid memory access). Signal: A signal is a software-generated interrupt that is sent to a process by the OS because when the user press ctrl-c or another process tells something to this process. There is fix set of signals that can be sent to a process. Signals are identified by integers. A signal number has symbolic names. System call: The interface between a process and an operating system is provided by system calls. System calls are usually made when a process in user mode requires access to a resource. Then it request...

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